Historically, surgical incisions in tissue have been performed with sharp metal cutting instruments. More recently, lasers have become the tool of choice in many medical procedures to cut and treat tissue. Laser beams can be accurately focused on tissue to cut many desired shapes and depths. The slit incision, a very narrow elongated incision, is especially appropriate for laser surgery. Surgeons can make these narrow incisions by passing a focused laser beam over the target tissue.
One medical procedure where slit incisions are desired is hair transplants. Hair transplants have become a common cosmetic procedure, particularly for the treatment of male pattern baldness. In a hair transplant procedure, a piece of the patient's skin having healthy growing hair is removed from a donor region on the scalp and implanted into a hairless, recipient region. This process involves cutting a hole or slit into the recipient region so that the new plug of hair can be inserted. Slit grafting is modernly used because of its many cosmetic and medical advantages over circular punching.
Historically, slit grafting has been accomplished by cutting a slit into the recipient region with a scalpel. More recently, lasers have been used. A laser is more advantageous because the size and shape of the incision can be more accurately controlled. A laser beam, usually a pulsed infrared beam, is focused onto the scalp. The exposure can be controlled to remove the amount of skin needed for the hair graft dimensions. Another advantage of using lasers to cut or remove skin is the coagulating effects of the laser light that minimizes bleeding and pain. Further, the laser radiation removes the skin in the slit it creates thereby creating room for the new plug of hair to be placed inside. This eliminates the compression problems involved with inserting a plug of hair in a narrow slit created with a scalpel. The use of lasers for hair transplants is further discussed in the applicant's co-pending application, "Laser Assisted Hair Transplant Method", application Ser. No. 08/012,895, filed Feb. 3, 1993.
A laser beam can be accurately focused on the scalp by a variety of optical delivery systems. One such system is marketed by the assignee in conjunction with its sealed carbon dioxide medical laser system under the name Ultrapulse 5000. The Ultrapulse system includes an articulated arm to direct the laser beam to its intended target. This articulated arm is composed of multiple successive straight segments connected by rotatable joints. In each joint there is an optic or a set of optics. A laser beam enters the first segment of the articulated arm toward the first joint. The beam is redirected by the optic(s) in that joint down the center of the next segment. The beam continues down successive segments being redirected at each joint. The beam is directed to its intended target through the last segment by the last optic in the last joint of the articulated arm. All the joints can rotate while maintaining beam alignment down the successive segment. Therefore, the user can direct the beam using the last segment of the arm to any target location in any angle desired.
To create a slit using the articulated arm, the surgeon positions the output segment of the articulated arm so that the beam will impinge on the target tissue. The surgeon then presses a footswitch which opens a shutter that allows light to exit the delivery end of the articulated arm. The doctor then moves the delivery end over the target tissue until the desired slit width and depth is created.
The drawback to this or most other optical delivery systems is that it takes time and skill to create a slit or series of slits of the desired dimensions. The doctor must-time the exposure and the speed of movement of the arm to remove the proper amount of skin in the scalp while ensuring the slit is consistent throughout its length. Since the number of slits required can be as numerous as the number of individual hair follicles being transplanted, the time and skill required to create accurate slits in the recipient area can be great.
There is a need for an optical delivery system that creates a slit of proper dimensions with as little as one single stationary exposure.
One method of achieving this goal is to impinge an elliptically shaped beam on the target tissue. In the prior art, elliptical beam profiles have been used to cut slit incisions in eyes. In this prior system, discussed in U.S. Pat. No. 5,152,759, the beam was transformed from a round beam to an elliptical beam by the use of a slit mask. More specifically, a beam having a circular cross-section is passed through a slit. The portion of the beam transmitted through the slit will have an elliptical cross-section. The drawback of this method is that it is inefficient. Laser power is wasted because much of laser beam is blocked by the slit mask to create the resulting elliptically shaped beam. While the loss of laser power may not have been significant for applications in eye surgery, tissue ablation requires higher power beams and therefore the use of a slit mask would not be suitable.
Another drawback of slit masks is that light which is not transmitted through the slit must be either reflected or absorbed by the mask creating further complications.
There is a need for an optical delivery system that creates an elliptical beam without any significant loss of laser power in the delivery and beam shaping system.